The present invention relates to an apparatus and a method for determining occurrence of a knock in an internal combustion engine.
A knock determining apparatus of a typical internal combustion engine includes a knock sensor attached to the cylinder block of the internal combustion engine. The knock sensor detects vibration of the cylinder block caused by a knock. The determining apparatus extracts the knock frequency component from an output signal of the knock sensor by a bandpass filter and compares a peak value of the knock frequency component or an integral of the knock frequency component during a predetermined interval with a knock determination threshold value to perform knock determination.
A knock is prevented by retarding the ignition timing, but retarding the ignition timing deteriorates the engine output and the fuel economy. Therefore, it is required to advance the ignition timing within a range of knock noise tolerable to the human ear and improve the engine output and the fuel economy. Therefore, the knock determination threshold value needs to be adapted to a value that permits detecting only a knock exceeding the permissible level to the human ear.
From this aspect, Japanese Examined Patent Publication No. 6-60621 discloses an apparatus that corrects the knock determination threshold value such that the distribution of a value obtained by the logarithmic conversion of the peak value of an output signal of the knock sensor will have a predetermined profile.
However, in the distribution that only uses the peak value of the output signal of the knock sensor, when a mechanical or electrical noise overlaps the output signal of the knock sensor, the distribution profile is formed that is similar to the profile made when a knock occurs. This deteriorates the correction accuracy of the knock determination threshold value, thereby deteriorating the knock determination accuracy.